1. Field of Invention
The invention relates to a spreading factor communication method and, in particular, to a spreading factor communication method that generates spreading codes.
2. Related Art
The rapid development of mobile phones all over the globe has spawned great advances in the wireless communication technology. The success of the widely used second generation (2G) mobile communication system nowadays does not only influence modern life, but also speeds up the development of the third generation (3G) mobile communication system. In the 3G wireless communications, important techniques include CDMA2000, the wideband-CDMA (W-CDMA) compatible with the 2.5G GSM network, and the China TD-SCDMA, all based upon the code division multiple access (CDMA).
However, people are not completely satisfied with the so-called 3G technology. With higher demands for wireless communications and to provide better services, many international manufacturers have started researches in more advanced techniques, called the beyond 3G techniques. These techniques will fix problems in the 3G system. For example, they will increase the usage efficiency of the frequency spectrum, the bandwidth of transmissions, the transmission speed. They will further have time vision duplex (TDD), global roaming, and higher service quality.
For example, the high speed and multirate properties in the 3G system are those beyond the reach of a 2G system. However, in order to have higher bit transmission ability, multicarrier modulation techniques have been proposed. This is because the multicarrier modulation techniques have the advantages of avoiding multipath attenuation and suppressing narrow column bandwidth interference. Incorporating the multicarrier modulation techniques into the CDMA technology is therefore an important part of the 3G wireless communications.
An issue that determines whether the beyond 3G wireless communication will be successful is how to effectively integrate the multicarrier modulation techniques with the original CDMA technology.
For example, in the spreading applications of one base station to multiple mobile stations, one mobile station has to use multiple spreading codes for encoding and decoding data in multiple carriers in order to have spreading data transmissions. In this case, to achieve the multirate transmission requirement, the base station has to allocate spreading codes of different lengths to mobile stations with different transmission speed needs or providing a mobile station with multiple spreading codes. To avoid interference among the spreading codes of different lengths, an ideal method is to let all mobile stations use spreading codes orthogonal to each other. Nonetheless, how to effectively allocate and transmit the spreading codes to the mobile stations determines the cost for constructing the whole communication system.
Since the communication bandwidth is very precious, directly transmitting spreading codes with a huge amount of data to the mobile stations during the communication process is very uneconomic. On the contrary, if all available spreading code tables, such as a whole code tree, are stored at the mobile stations, the cost of the equipment will increase, restricting its applications on the market.
In summary, how to find a spreading code generating and transmission method for the multicarrier and multirate CDMA system is a valuable work in the field.